Nucleotide metabolism is different in vascular and lymphatic endothelial cells. (A) Vascular human dermal microvascular endothelial cells (HDMEC) were incubated 45 minutes with 20μM [³H]AMP in the presence of 20μM APCP, 250μM ATP, and 100μM Ap₅A (as indicated on lanes 2-5), separated by TLC and developed by autoradiography. In another experiment, vascular and lymphatic cells were incubated for 25 minutes with 20μM [³H]AMP (lanes 6, 7). Blanks (Bl) show the radiochemical purity of [³H]AMP (lanes 1, 8), and arrows indicate the positions of nucleotide and adenosine standards. (B) Activities of ATPase, ADPase, ecto-5′-nucleotidase (5′-NT), and adenylate kinase were determined in vascular and lymphatic endothelial cells by using saturating concentrations of ³H-labeled nucleotide (mean ± SEM; n = 5). *P < .05. (C) Expression of CD73 on podoplanin-positive (lymphatic, left) and -negative (blood vessel, right) endothelial cells analyzed by FACS.